Method and apparatus for annealing coils of metal strip



y 9, 1951 R. E. MCCLURE, JR 2,983,502

METHOD AND APPARATUS FOR ANNEALING cons 0F METAL STRIP 3 Sheets-Sheet 1 Filed Oct. 21, 1953 y 9, 1951 R. E. MCCLURE, JR 2,983,502

METHOD AND APPARATUS FOR ANNEALING cons 0F METAL STRIP Filed Got. 21, 1953 3 Sheets-Sheet 2 h weniom' P055275 /%Q (/25,

M y 9, 1951 R. E. MCCLURE, JR

METHOD AND APPARATUS FOR ANNEALING COILS OF METAL STRIP 3 Sheets-Sheet 3 Filed 00%... 21, 1953 FIEIiseveral bases.

insulating cover thereover.

"METHOD AND APPARATUS FOR ANNEALING COILS F METAL srmr- Robert E. McClure, Jr., Pittsburgh, Pa., assignor to }Jnited States Steel Corporation, a corporation of New ersey v 7 Filed Oct. 21, 1953, Ser. No. 387,487 10 Claims. (Cl. 263-40) This invention relates to a metallurgical furnace and method. In particular, it is concerned with the heating of metal strip in coils for the purpose of annealing.

' "In modern steel-mill practice, cold-reducedsteel strip 'a serious objection thereto,'viz., the relatively slow rate at.which heat penetrates to the center of the charge through the wall of the'inner cover and the successive plies or thicknesses of the strip making up the coils. As a result, both heating and cooling stages of the annealing cycle vare quite long and the production from a single hood is limited, even though it is used successively with What is more serious, there is a large temperature differential between different parts of the charge as it heats up, causing non-uniformity in-the characteristics of the finished product.

2,983,502 Patented May 9, 1961 ice hating the present preferred embodiment In the drawings, t

Fig. 1 is a plan view showing in horizontal section a.

portion'of a cover-type furnace equipped according to the invention; I

.Many attempts have been made to remedy the above I difiiculties. Fans have been installed in the base supporting the charge, for circulating at high velocity the protective atmosphere usually introduced into the inner cover, to increase convection heating of the charge. addition, convector spacers have been used between coils .to permit some circulation of the atmosphereacross the ends of the coil turns and thereby increase the rate of heat absorption. Even. with these expedients, all the by the inner cover and then transmitted from it to the charge by radiation or convection.

I have invented a novel system of heating a charge of stacked coils enclosed within an insulating cover and an inner metal cover. In accordance with my invention I generate heat within the inner cover in immediate proximity to the ends of the coils thereby effecting'a rapid penetration of heat into the interior of the charge. More particularly, the invention contemplates portable, panheat delivered to the charge must still be absorbed first Figure 2 is a longitudinal section taken along the plane of line 11-11 of Figure 1'; I

Figure 3 is a transverse section taken along the plane of line III-III of Figure 1; and v Figure 4is a plan view of an element for heating the portable plates or chambers. 1

Referring now in detail to the drawings, a furnace comprises a base or hearth 11 and a hood or coverx12 adapted to be placed over a charge deposited thereon making a tight seal with the base by virtue of interfitting channels and flanges 13. The base and cover are fabricated from steel plate and rolled sections and each has a refractory lining. Charge supports or hearthvplates @214 of heat-resistant steel are laid on the base and each is adapted to receive a stack-of coils C of; metal strip disposed with their axes vertical and substantially coinciding. 1

In accordance with my invention, I intersperse heatgenerating means with the coils C stacked on supports 14.- Preferably, I place a heating plate or chamber 15 on each support, then deposit'a ooil C on the plate. A second plate is set on the coil and a second coil on the second plate and so on until each stack '16 of the furnace .charge has been built up to the desired height. The heating plate 15 as illustrated is in the form of an annular chamber or fire-box comprising a pair of vertically spaced bearing plates 17 and 18 having coaxial cylindrical spacers 19 and 20 therebetween- The top plate 17 is removable from the spacers. Radial webs 21 spaced circumferentially of each chamber support an annular combustion tube 22 in a plane parallel to' plates 17 and 18. i In order to supply heat-generating media to the tubes 22'between the bearing plates of the fire boxes, I provide a riser 23 adjacent each stack 16 extending upwardly through base 11 and secured thereto. Each riser includes an outlet'main 24 for waste combustion gases, an air-inlet main 25 extending therethrough, and a fuelsupply main 26 adjacent thereto. Air is supplied to .mains 25 from a blower 27 through a header 28. The fuel supply mains are connected to a header 29 from any convenient source of gas. Outlet mains 24 are connected to an exhaust header 30 extending to a stack (not shown). Mains 24 and 25 are in heat-exchange relation whereby the outflowing waste gases preheat the incoming combustion air.

calke heating plates or chambers fitted with heat-gem crating means, adapted to be placed on one coil and to support another coil thereon. Connections for supplying heat-generating media to the plates extend upwardly through the base on which the charge is stacked. Heating plates and coils are preferably stacked alternately on the base and enclosed by lowering the inner cover and Heat is then generated in the space between the coils and transmitted directly thereto by radiation and conduction. At the conclusion of the heating andcooling stages, the coils are removed from the base and the heating plates are taken-off piled alternately with the next batch of coils.

q ,yAs shown in Figure 4, the ends of each tube 22 extend I radially thereof at a common point, one end 31 extending la'terallyinto and thence through the other 32 which is enlarged to accommodate it. A burner nozzle 33, is -mountedvon a fitting which closes tube end 31 and is connected to fuel-supply main '26 by flexible metallichose 34'equipped with quickly detachable couplings 35. .A similar flexible metallic-hose 36 fitted with similar couplings connects the outlet end 32 of tube 22 to outlet :main 24. A flexible metallic-hose 37 also fitted 'With quickly detachable couplings (not shown) extends through hose 36 and connects air-main 25 to the inlet end 31 of tube 22. The hoses'34, 36 and 37 are of heatresistant steel. v They permit the heating plates to be piled with coils of various widths.

After the heating chambers'15 and coils have been stacked alternately on change supports 14 and connections made between the ends of tubes 22 and the outlet, air

and fuel mains 24, 25 and 26, an inner cover 38 is lowered over each stack 16 and the insulating cover is low- 'ing stage of the annealing cycle. been cooled to the proper temperature, usually that at which the strip does not oxidize readily in air (about 300 F.) covers 38are removed and the coils are unloaded from the stacks 16. This involves laying the heating by many important advantages.

heat is absorbed by the charge.

effects a further shortening of the annealing cycle. As a.

cred onto base 11. Blower 27 is then driven as by a motor 39 and valves 40 in the lines leading to fuel mains 26 are opened. As a result, a combustible mixture is delivered to tubes 22 andcirculated therethrough. A

spark-gap igniter 41 at the lower end of each outlet rna'in 24 initiates combustion of the mixture whereupon the flametravels back along the course of the gases'to the tips of burners 33. 22 by combustion of the gases fired therethrough and the heatis radiated'frorn the tubes to plates 17 and 18. t The latter conduct the heat directly to' the edges of the. coil turns exposed to contact with the plates. A protective atmosphere may be maintained in the inner covers by inlet 42 and outlets 43 extending through the base 11.

The supply of fuel is controlled as the charge temperature rises, toprevent overheating when the final temperature is' reached. It is also graduated downwardly as by permost one to prevent overheating the upper coilsof the stack. When the charge has been brought up to the desired temperature and held thereat for the required time,

valves 40 are closed to terminate the generation of heat sired, to cool the charge by circulation of atmospheric air through the tubes. This, of course, shortens the cool- When the charge has plates or chambers 15 aside temporarily, after breaking the couplings 35. As soon as one charge has been unloaded from the base, another may be loadedon and the heating thereof started without delay, the heating plates being placed-alternately with the coils and their tubes 22 reconnected to the mains before the inner covers 38 and insulating cover 12 are replaced.

- 'It will be evident that the invention is characterized The principal one is the time saving made possible by the increased rate at which The forced cooling also result of the time'thus saved, a furnace according to my invention has a greater capacity per weekthan conventional radiant-tube furnaces. There is also less difference between the temperatures of the hottest and coolest portions of the charge thus improving the uniformity of;

the product. The combustion air is heated by the outflowing waste gases thereby increasing combustion efiiciency and fuel economy.

My portable heating elements alford better support for the combustion tubes 22 than is possible for the tubes in conventional furnace construction. The aggregate length of the tubes, furthermore, is less. This decreases the cost of the equipment. Contributing further to the latter -is the omission of the atmospheric-circulating fan and spacers found necessary in conventional radiant-tube furnaces.

Although I have disclosed herein but a preferred embodiment of my practice,'I intend to cover as Well any change or modification therein which may be made with-. out departing from the spirit and scope of the invention.

I claim: 1. In a method of heating coils of metal strip, the steps including placing a coil with its axis vertical on a hearing surface, placing on said coil a pair of bearing plates spaced apart, one overlying the other, placing a second coil on the upper of said last-mentioned plates, enclosing the resulting stack, discharging and igniting a combustible mixture of gases around the space between said pair of plates and exhausting burned gases from said space there Thus heat is generated in the tubes 9 orifice plates, from the bottom heating plate to the upby heating said coils principally by conduction through said plates directly into the edges of the coil plies in contact therewith. 1

2. In a method of heating coils of metal strip, the steps including stacking coils in vertically spaced relation with their axes substantially in vertical alinement, disposing an annular radiant tube in the space between each pair of adjacent coils, enclosing the stacked coils, discharging and igniting a combustible'mixture of gases through said tubes thereby supplying heat to the coils principally throughthe edges of the plies thereof, and exhausting burnedgases from said tubes.

v 3. In apparatus for heating coils of metal strip including a hearth, a cover disposable thereon to enclose a stack of coils built up on the hearth,.the combination therewith of a plurality of independent annular fire boxes disposed one beneath each coil, fuel and air mains extending through said hearth and detachable connections between said mains. and each fire box.

4. The apparatus defined by claim 3 charaoterize d by an exhaust main extending upwardly through said base for conducting waste gases from the fire boxes and detachable connections from said exhaust main to. each fire box.

5, The apparatus defined by claim 3 characterized by each fire box having an annular radiant tube therein, said connections extending to said tubes.

6 The apparatus defined by claim 5 characterized by said tubes having entering and exit end portions extendfing radially through said fire boxes.

.7. In apparatus for heatingcoils of metal Strip includling a hearth, a cover disposable thereon to enclose a stack of coils built up on the hearth, the combination therewith ofa plurality of pairs of vertically spaced hearing plates adaptedto be disposed one pair beneath each coil, fuel and air mains extending upwardly through said hearth and a burner firing into the space between each .pair of plates, said burners being connected to said mains.

8. The apparatus defined by claim 7 characterized by an annular radiant tube "disposed in a horizontal plane 'betweenthe plates of each pair, said burners firing into said tubes, respectively.

9. A portable heater adapted to be placed horizontally between adjacent coils piled one on another to form a stack, said heater comprising a chamber having a central passage therethrough, said chamber being defined by spaced upper and lower bearing plates, and spaced inher and outer tubular load-transmitting walls extending between said plates, an annular radiant tube disposed co axially in said chamber in a plane parallel to said plates I and spaced vertically from each of said plates, and a burnsaid tube at a level intermediate said plates.

7 References Cited in the file of this patent UNITED STATES PATENTS 2,671,656 Winder Mar. 9, 

